Ecuador's Sangay, isolated on the east side of the Andean crest, has exhibited frequent eruptive activity over the last 400 years. Its remoteness has made ground observations difficult until recent times, and thus most information has come from aviation reports from the Washington Volcanic Ash Advisory Center (VAAC) and MODIS (Moderate Resolution Imaging Spectroradiometer) satellite-based data. Thermal anomaly information is reported by the University of Hawaii's MODVOLC system and the Italian MIROVA Volcano HotSpot Detection System. Ecuador's Instituto Geofísico (IG) issues periodic Special Reports of activity. This report summarizes the intermittent nature of the eruptions from 2011-2013, and covers renewed activity during January 2015 through July 2017.

Summary of activity during 2011-2013. Activity during 2011 (figure 14) began with a continuation of the intermittent ash emissions and thermal anomalies that persisted throughout 2010 (BGVN 36:01). Ash plumes during January and February 2011 were reported at typical altitudes between 6 and 8 km; thermal alerts appeared once each during January and March. No activity was reported after 2 March until a new series of thermal alerts began more than 3 months later on 6 June 2011; they were intermittent from then through 19 September 2012, with reports occurring during 1-4 days of all but three months. Ash emissions were also intermittent during this time, with VAAC reports issued during eight of the months from 2 August 2011-28 July 2012 for plumes reported at altitudes of 6-8 km. They also generally occurred during 1-4 days of the month. A four-month break in activity followed until ash plumes were reported on 25 January 2013; they were intermittent until 24 May 2013. MODVOLC thermal anomalies were also reported during this time, on 2 February, 25 March, and 3-4 May.

Figure 14. Summary chart of ash emissions and thermal anomalies reported from Sangay during January 2010 to early August 2017. Red bars show eruptive periods where there are reports of either ash plumes or thermal anomalies without a lack of observed activity for more than 3 months. Rows with pink cells indicate dates with thermal anomalies (MODVOLC or MIROVA). Rows with blue cells indicate dates with ash emissions as reported by the Washington VAAC. A range of dates means that activity occurred at least on those two dates, but may not have been continuous. Data courtesy of Washington VAAC, HIGP MODVOLC Thermal Alerts System, and MIROVA.

Summary of activity during January 2015-July 2017. After 19 months of quiet from June 2013 through December 2014, an ash plume reported on 19 January 2015 marked the beginning of a new eruptive episode that included ash plumes, lava flows, and block avalanches between 19 January and 7 April 2015. The next reported activity included both ash emissions and thermal anomalies observed almost a year later on 25 March 2016, although IG had reported increases in seismicity during the previous two weeks. Ash emissions and thermal anomalies were intermittent through 16 July 2016. There was a single thermal anomaly seen in MIROVA data on about 10 October and a brief ash emission occurred during 16-17 November 2016, after which Sangay was quiet until a new episode started on 20 July 2017 that was ongoing into August.

Activity during January-April 2015. After a 19-month period of no reported activity (since May 2013), ash emissions were again seen beginning on 18 January 2015 when an ash plume rose to 6.4 km altitude and drifted SW. Additional plumes on 25 January and 4 February rose to 7.3 km and 6.7 km, respectively, and drifted less than 20 km SW (figure 15). Ash plumes primarily observed by pilots between 27 February and 16 March were generally not visible in satellite images due to weather clouds. During this episode, MODVOLC thermal alerts were reported on 26 January; 7, 21, 23 and 27 February; 2,4,18, and 27 March; and 1, 3, and 7 April.

In a March 2015 report, IG noted that new lava flows and block-avalanche deposits had been emplaced during January and February 2015. The lava flows descended the SE flank about 900 m (figure 16). Two areas of deposits from block avalanches and ashfall extended 2.5 km ESE from the lava front, and 1.5 km down the S flank. According to IG, there were 21 thermal anomalies identified in MIROVA during 31 January-25 February 2015.

Figure 16. Locations of lava flows and block-avalanche deposits at Sangay that were emplaced during January and February 2015. The new lava flows are shown in red. The ash and block-avalanche deposits are shown in stippled yellow/green. Courtesy of IG (Informe Especial del Volcan Sangay No 1, 16 March 2015).

Activity during March-November 2016. IG reported an increase in seismicity on 5 March 2016, after ten months of no reported activity. An explosion signal was followed by harmonic tremor on 9 March, and IG noted that both a thermal anomaly and an emission drifting S were identified in NOAA satellite images. They inferred that increased seismic "explosion" signals on 14 March were indicative of ash-and-gas emissions, although weather clouds prohibited visual confirmation. Ash emissions rising to 6.1 km altitude were first reported by the Guayaquil MWO on 25 March 2016; they noted two more emissions on 27 and 28 March rising to similar altitudes (7.6 and 6.4 km, respectively), but cloudy weather prevented satellite confirmation. Plumes reported on nine days during April rose to similar altitudes (ranging from 5.5-7 km) and extended 18-30 km N or NW from the summit. A series of daily emissions occurred from 30 April-7 May. The emissions included a plume on 2 May that extended 120 km NW, and one on 6 May that rose to 8.2 km altitude and extended approximately 55 km SW before dissipating. Ash-bearing plumes were reported on 10 more days during the rest of May.

Although no more ash plumes were reported until 16 July 2016, MODVOLC thermal alerts were persistent every month beginning on 25 March and lasting through 5 July (see figure 14 above). The MIROVA data for this period also clearly show persistent thermal anomalies (figure 17). A short-lived eruption event during 16-17 November 2016 consisted of an ash emission that rose to 6.1 km altitude and drifted as far as 290 km SE.

Figure 17. Thermal anomaly data from MIROVA for the year ending on 18 January 2017 at Sangay, showing the eruptive episode of March-July 2016, and a brief anomaly on about 10 October 2016; late October-November anomalies are more than 20 kilometers from the summit and unrelated to volcanism. Courtesy of MIROVA.

Activity beginning July 2017. A new eruptive episode began on 20 July 2017, after eight months without major surface activity. Low-energy ash emissions rising to 3 km above the crater, incandescent block avalanches on the ESE flank (figure 18), and a possible new lava flow were reported by IG. The Washington VAAC reported an ash emission on 20 July rising to 8.2 km altitude and drifting about 80 km W. A plume was reported on 1 August by the Guyaquil MWO but obscured by clouds in satellite images, and a plume on 2 August was seen in webcam images (figure 19).

Figure 18. Incandescent blocks roll down the ESE flank of Sangay during the early morning of 1 August 2017. Courtesy of IG (Informe Especial del Volcán Sangay-2017-No 1, 3 August 2017).

Based on satellite and model data, and information from the Guayaquil MWO, the Washington VAAC reported that ash plumes from Sangay rose to altitudes of 6.1-8.5 km (20,000-28,000 ft) a.s.l. The plumes drifted NW on 2 September.

Based on satellite data, the Washington VAAC reported that a plume from Sangay with possible ash content rose 7 km (23,000 ft) a.s.l. and drifted over 30 km SW. A thermal anomaly was identified on 23 August.

Based on information from IG, the Guayaquil MWO, and satellite data the Washington VAAC reported continuing ash emissions at Sangay. On 16 August an ash plume drifted W. On 17 August an ash plume rose to an altitude of 8.2 km (27,000 ft) a.s.l. and drifted NW, and was followed by several more ash puffs. During 19-20 August ash plumes rose to 5.8 km (19,000 ft) a.s.l. and drifted SW and W. A thermal anomaly was identified in satellite images on 20 August.

Based on information from the Guayaquil MWO, the Washington VAAC reported that on 12 August an emission from Sangay rose to altitudes of 6.1-6.4 km (20,000-21,000 ft) a.s.l. and drifted SW and NW. Ash in the emission was not detected in satellite data. On 13 August satellite data showed a well-defined thermal anomaly over the volcano, and an ash plume drifting 55 km SW.

In a special report from 3 August, IG reported that a new eruptive phase at Sangay began on 20 July, after 8 months without major surface activity. The recent activity was characterized by low-energy ash plumes rising no more than 3 km above the crater rim, incandescent rocks rolling as far as 1 km down the ESE flank, and a possible lava flow on the same flank. Minor amounts of ash fell in uninhabited areas to the W.

Based on Washington VAAC reports, IG noted two ash plumes on 20 July and one on 2 August that rose 2.3-3 km above the crater and drifted W and NW. Numerous thermal anomalies detected during 2-3 August were aligned on the ESE flank. Based on numerical weather prediction (NWP) models, satellite data, and information from the Guayaquil Meteorological Watch Office (MWO), the Washington VAAC reported that on 6 August an ash plume drifted W.

Based on satellite images and wind data, the Washington VAAC reported that during 16-17 November ash plumes from Sangay rose to an altitude of 6.1 km (20,000 ft) a.s.l. and drifted as far as 290 km SE.

Based on satellite images and wind data, the Washington VAAC reported that during 25-27 and 30-31 May ash plumes from Sangay rose to altitudes of 5.8-6.7 km (19,000-22,000 ft) a.s.l. and drifted NE, E, SW, and W. A hotspot was detected during 26-27 May.

IG reported that at the beginning of March Sangay began a new phase of activity which continued through at least 12 May without significant changes. The number of tremor events and long-period earthquakes were slightly higher in March as compared to the number recorded in April and May, and the number of explosions was slightly higher in April and May. Surficial activity was characterized by frequent ash emissions generated by explosive activity. Thermal anomalies on the flanks were also detected, mostly within 5 km of the summit crater, which possibly corresponded to short-range pyroclastic flows and lava flows. No abnormal sulfur dioxide emission were detected.

Based on satellite images, notices from the Guayaquil MWO, and information from IG, the Washington VAAC reported that during 4-7 and 9-10 May ash plumes from Sangay rose to altitudes of 6.1-8.2 km (20,000-27,000 ft) a.s.l. and drifted as far as 55 km NW, W, WSW, and SW. An intermittent thermal anomaly was identified in satellite images during 4-5 and 10 May.

Based on satellite images and notices from the Guayaquil MWO, the Washington VAAC reported that during 27 April-3 May ash plumes from Sangay rose to altitudes of 5.8-7 km (19,000-23,000 ft) a.s.l. and drifted as far as 120 km WNW, W, and S. A thermal anomaly was identified in satellite images during 29-30 April and on 2 May.

The Washington VAAC reported that on 15 April an intermittent thermal anomaly was identified in satellite images over Sangay. No ash was detected in images, though seismic data indicated activity. On 19 April the Guayaquil MWO indicated that an ash plume rose to an altitude of 6.1 km (20,000 ft) a.s.l. and drifted W.

Based on satellite images and notices from the Guayaquil MWO, the Washington VAAC reported that on 1 April an ash plume from Sangay rose to an altitude of 6.7 km (22,000 ft) a.s.l. and drifted SW. The next day an ash plume rose to an altitude of 5.5 km (18,000 ft) a.s.l., and a continuing thermal anomaly was detected. On 4 April satellite images detected an ash plume that drifted about 18 km N at an altitude of 5.5 km (18,000 ft) a.s.l.

Based on notices from the Guayaquil MWO, the Washington VAAC reported that on 25 March an ash plume from Sangay rose to an altitude of 6.1 km (20,000 ft) a.s.l. and drifted W. On 27 March a pilot observed an ash plume rising to an altitude of 7.6 km (25,000 ft) a.s.l. and drifting W. The next day an ash plume rose to an altitude of 6.4 km (21,000 ft) a.s.l. and drifted WSW. Cloud cover prevented satellite observations of the volcano on all three days.

IG reported that tremor at Sangay ceased on 10 March and the number of long-period earthquakes began to decline the next day. The number of explosions per day increased (from a maximum of four during 3-11 March) to 10 on 12 March, peaked at almost 110 on 15 March, and then declined to 50 on 17 March. Cloud cover prevented views of the volcano though the seismic data suggested that gas-and-ash emissions were produced; ashfall was not reported in towns downwind. At 0400 on 17 March continuous tremor with interspersed bursts of more intense tremor began to be detected. The activity intensified at 1300, and then began to gradually decline. IG noted that climbers should avoid the volcano during periods of increased activity.

IG reported that the seismic network at Sangay started to record sporadic seismic events on 5 March, although seismicity became more notable during 8-9 March; signs of small explosions and volcano-tectonic events were detected on 7 March, and long-period signals emerged on 9 March. An explosion signal was followed by harmonic tremor on 9 March. That same day satellite images detected a thermal anomaly and an emission that drifted S.

Based on a SIGMET notice of a pilot observation, the Washington VAAC reported that on 26 February an ash plume from Sangay rose to an altitude of 7.3 km (24,000 ft) a.s.l. Satellite images only detected an intermittent thermal anomaly. According to the VAAC, on 27 February IG reported a lava flow and a possible diffuse ash plume that rose to an altitude below 5.5 km (18,000 ft) a.s.l. within 15 km of the summit. On 2 March a local pilot observed an ash plume that rose to an altitude of 7.6 km (25,000 ft) a.s.l. On 3 March an ash plume rose to an estimated altitude of 5.2 km (17,000 ft) a.s.l. and drifted 13 km W.

Based on a pilot observation, the Washington VAAC reported that on 4 February an ash plume from Sangay rose to an altitude of 6.7 km (22,000 ft) a.s.l. Satellite images showed a possible ash plume drifting less than 20 km SW. A thermal anomaly was visible in satellite images the next day, as well as a diffuse plume with possible ash drifting W.

Based on a pilot observation, the Washington VAAC reported that on 25 January an ash plume from Sangay rose to an altitude of 7.3 km (24,000 ft) a.s.l. Weather clouds prevented satellite image confirmation of the plume, although a thermal anomaly was detected which continued through the next day.

Based on a pilot observation, the Washington VAAC reported that on 18 January an ash plume from Sangay drifted SW at an altitude of 6.4 km (21,000 ft) a.s.l. Weather clouds prevented satellite image views of the plume, although a thermal anomaly was detected. A faint thermal anomaly was detected the next day.

Based on a pilot report, the Washington VAAC reported that on 23 May an ash plume from Sangay drifted W at an altitude of 7.6 km (25,000 ft) a.s.l. Weather clouds prevented satellite image views of the plume.

Based on analyses of satellite imagery and a SIGMET aviation notice, the Washington VAAC reported that on 26 April two brief ash emissions from Sangay drifted SW and dissipated within 20 km. A thermal anomaly was visible in infrared satellite images.

According to the Washington VAAC, on 22 February a pilot observed an ash plume from Sangay that rose to an altitude of 7.6 km (25,000 ft) a.s.l. and drifted SW. Due to cloud cover in the area, neither satellite image analysis nor the Instituto Geofísico-Escuela Politécnica Nacional (IG) could confirm an ash emission. Ash plumes were not detected in cloudy satellite image views during 23-24 February, but a thermal anomaly was detected on 24 February.

Based on a pilot report, analyses of satellite images, and information from the Guayaquil MWO, the Washington VAAC reported that a possible eruption from Sangay before 1210 on 25 January may have produced ash plumes. Cloud cover prevented satellite observations of emissions during 25-26 January, although a weak thermal anomaly was detected.

According to the Washington VAAC, a pilot reported that on 29 July an ash plume from Sangay rose to an altitude of 6.7 km (22,000 ft) a.s.l. and drifted W. A plume that may have been mostly gas was detected in satellite images pushing through the metrological cloud deck and drifting W.

According to the Washington VAAC, a pilot reported that a possible eruption from Sangay occurred prior to 1438 on 20 July. Ash was not observed in satellite imagery and a SIGMET issued for the event was later cancelled.

According to the Washington VAAC, a pilot observed an ash plume from Sangay on 6 June that rose to an altitude of 6.1 km (20,000 ft) a.s.l. and drifted N. Meteorological clouds prevented satellite image views. A pilot observed ash drifting E on 10 June.

Based on a SIGMET report, the Washington VAAC reported a possible eruption and ash plume from Sangay on 28 May. A later notice stated that a pilot reported an ash plume at an altitude of 6.1 km (20,000 ft) a.s.l. Ash was not identified in satellite imagery.

Based on information from pilots and the Guayaquil MWO, an ash plume from Sangay was reported drifting S and SE on 23 January. Ash was not detected in partly-cloudy satellite imagery. On 24 January a hotspot was visible on satellite imagery.

The Washington VAAC reported that on 20 November an ash plume from a possible eruption at Sangay was observed by a pilot and drifted at an altitude of 5.9 km (19,500 ft) a.s.l. Ash was not detected in partly-cloudy satellite imagery.

Based on analyses of satellite imagery, the Washington VAAC reported that on 25 October a gas plume from Sangay, which possibly contained ash, drifted 75 km E. Ash was not identified in subsequent images.

Based on information from the Guayaquil MWO and a pilot observation, the Washington VAAC reported that on 11 October an ash plume from Sangay from a possible eruption rose to an altitude of 6.7 km (22,000 ft) a.s.l. and drifted W. Ash was not observed in satellite imagery.

Based on a pilot observation, the Washington VAAC reported that on 12 January an ash plume from Sangay rose to an altitude of 6.7 km (22,000 ft) a.s.l. and possibly drifted more than 45 km SW. A thermal anomaly was detected in satellite imagery.

The Washington VAAC reported that on 21 September an ash plume from Sangay rose to an altitude of 7.6 km (25,000 ft) a.s.l. and was observed by a pilot. Ash was not seen in satellite imagery, although weather clouds were in the area.

The Washington VAAC reported that on 10 September a small plume and a thermal anomaly from Sangay were seen in satellite imagery. Based on information from Tegucigalpa MWO, pilot observations, and analyses of satellite imagery, the VAAC reported that on 13 September small plumes of gas with possible ash drifted SW. A thermal anomaly had also been detected for the previous few hours.

Based on analyses of satellite imagery, the Washington VAAC reported that on 19 August small ash-and-gas plumes from Sangay drifted about 25 km W and dissipated. Intermittent thermal anomalies were also detected. On 20 August a pilot reported an emission that was not seen in satellite imagery.

Based on pilot observations and analyses of satellite imagery, the Washington VAAC reported that on 21 July an ash cloud from Sangay drifted W. During 22-23 July, diffuse plumes drifted 65-115 km W. Occasional thermal anomalies were detected by satellite imagery on 21 and 23 July.

The Washington VAAC reported that on 6 May an ash plume from Sangay was seen by a pilot. Ash was not identified in satellite imagery, but a diffuse steam-and-gas plume was seen before weather clouds moved into the area.

Based on a pilot observation, the Washington VAAC reported that on 21 April an ash plume from Sangay rose to an altitude of 6.7 km (22,000 ft) a.s.l. Ash was not identified in satellite imagery, although weather clouds were present in the area.

Based on pilot observations, the Washington VAAC reported that on 2 February an ash plume from Sangay rose to an altitude of 8.2 km (27,000 ft) a.s.l. Ash was not identified in satellite imagery, although weather clouds were present in the area.

Based on pilot observations, the Washington VAAC reported that on 14 January an ash plume from Sangay rose to an altitude of 7.3 km (24,000 ft) a.s.l. Ash was not identified in satellite imagery, although weather clouds were present in the area.

The Washington VAAC reported that during 2-4 January thermal anomalies from Sangay were seen in satellite imagery. On 2 January, a pilot saw an ash plume drifting NW at an altitude of 7 km (23,000 ft) a.s.l. An ash plume was also reported by a pilot the next day.

Based on pilot observations, the Washington VAAC reported that on 18 and 21 December ash plumes from Sangay rose to an altitude of 7.9 km (26,000 ft) a.s.l. and drifted W. Ash was not identified in satellite imagery, although weather clouds were present in the area. Thermal anomalies were occasionally detected in the satellite imagery.

Based on a pilot observation, the Washington VAAC reported that on 1 December an ash plume from Sangay rose to an altitude of 7.9 km (26,000 ft) a.s.l. and drifted W. Ash was not identified in satellite imagery, although low weather clouds were present in the area. Later that day, an eruption was reported, but ash was again unidentifiable in satellite imagery.

The Washington VAAC reported that on 4 October a pilot saw an ash plume from Sangay drifting W at altitudes of 5.2-7.6 km (17,000-25,000 ft) a.s.l. Meteorological clouds prevented satellite views of the area. No additional reports of the ash plume were received by the VAAC.

Based on a pilot observation, the Washington VAAC reported that on 23 July a possible ash plume from Sangay rose to an altitude of 7.9 km (26,000 ft) a.s.l. The plume was not identified in satellite imagery.

Based on a pilot observation, the Washington VAAC reported that on 26 June an ash plume from Sangay rose to an altitude of 7.6 km (25,000 ft) a.s.l. The suspected ash was seen on satellite imagery drifting less than 30 km W.

Based on pilot observations and analysis of satellite imagery, the Washington VAAC reported that on 10 March an ash plume from Sangay rose to an altitude of 5.5 km (18,000 ft) a.s.l. and drifted W. A thermal anomaly was detected in satellite imagery.

Based on pilot observations, the Washington VAAC reported that on 9 February a plume from Sangay rose to an altitude of 7.9 km (26,000 ft) a.s.l. No ash was identified on satellite imagery, but meteoric clouds were also present in the area.

Based on a pilot observation, the Washington VAAC reported that on 5 January an ash plume from Sangay rose to an altitude of 7 km (23,000 ft) a.s.l. and drifted S. Ash was not identified on satellite imagery.

Based on observations of satellite imagery and pilot reports, the Washington VAAC reported that an ash plume from Sangay rose to an altitude of 6.1 km (20,000 ft) a.s.l. on 26 December and drifted SW. A thermal anomaly was seen on satellite imagery during 26-27 December.

Based on pilot observations, the Washington VAAC reported that an ash plume from Sangay rose to an altitude of 5.5 km (18,000 ft) a.s.l. and drifted W on 2 August. Ash was not detected on satellite imagery.

Based on pilot observations, the Washington VAAC reported that an ash plume from Sangay rose to an altitude of 6.7-8.2 km (22,000 to 27,000 ft) a.s.l. on 28 July. Ash was not detected on satellite imagery but a weak hotspot could be seen.

Based on pilot observations, the Washington VAAC reported that an ash plume from Sangay rose to an altitude of 5.5 km (18,000 ft) a.s.l. and drifted W on 23 July. Ash was not detected on satellite imagery. On 24 July, a diffuse ash plume at an altitude of 5.2 km (17,000 ft) a.s.l. was visible on satellite imagery drifting SW.

Based on pilot reports and satellite imagery, the Washington VAAC reported that an ash plume from Sangay on 17 March rose to an altitude of 5.2 km (17,000 ft) a.s.l. A hotspot was visible on satellite imagery. A pilot reported an ash plume on 20 March to an unreported altitude.

Based on information from IG, pilot reports, and satellite imagery, the Washington VAAC reported that eruptions from Sangay during 12-13 March produced ash plumes that rose to 7 km (23,000 ft) a.s.l. and drifted W. A hotspot was seen on satellite imagery.

Based on information from the Guayaquil MWO and satellite imagery, the Washington VAAC reported that an eruption from Sangay on 28 February produced an ash plume that rose to an altitude of 7.6 km (25,000 ft) a.s.l. On 2 March, a diffuse plume and a weak hotspot were seen on satellite imagery. On 5 March, a pilot reported that an ash plume rose to between 5.2-6.1 km (17,000-20,000 ft) a.s.l. and drifted W.

Based on information from Guayaquil MWO, IG, pilot reports, and satellite imagery, the Washington VAAC reported that eruptions from Sangay during 6-10 and 13 February produced ash plumes that drifted SW, NW, N, and W. Plumes reached altitudes of 9 km (30,000 ft) a.s.l. on 6 February and 6.1 km (20,000 ft) a.s.l. on 9 February. A hotspot was seen on satellite imagery at the summit during 7-9 and 13 February.

Based on information from the Guayaquil MWO and satellite imagery, the Washington VAAC reported that an eruption from Sangay on 6 February produced ash plumes that rose to a maximum altitude of 9.1 km (30,000 ft) a.s.l. and drifted SW.

Based on information from Guayaquil Meteorological Watch Office (MWO), pilot reports, and satellite imagery, the Washington VAAC reported that an eruption from Sangay on 14 January produced an ash plume that rose to an altitude of 6.1 km (20,000 ft) a.s.l. and drifted SW.

Based on information from Guayaquil Meteorological Watch Office (MWO) and satellite imagery, the Washington VAAC reported that an eruption from Sangay on 1 January produced an ash plume that rose to an altitude of 5.2 km (17,000 ft) a.s.l.

Based on pilot reports and satellite imagery, the Washington VAAC reported that an eruption from Sangay on 2 December produced an ash plume that rose to an altitude of 8.5 km (28,000 ft) a.s.l. and drifted SW.

An ash plume emitted from Sangay was visible on satellite imagery on 16 October around 0645. The plume moved SSW very slowly, corresponding to a possible height of ~6.7 km (22,000 ft) a.s.l. By 0900 the plume was too thin to be visible on satellite imagery and thunderstorms developed in the area, further obscuring the ash cloud.

According to the Washington VAAC, on 28 December around 0715 satellite imagery showed a plume from Sangay that was most likely composed of steam with little ash. The plume was E of the volcano's summit at a height of ~6.4 km a.s.l. A hotspot was prominent on satellite imagery, but ash was more difficult to distinguish.

According to the Washington VAAC, satellite imagery showed a plume emitted from Sangay on 14 January around 0500 extendeding ~45 km E. The plume most likely contained ash. During this time a hotspot was also visible on satellite imagery.

July 1975 (CSLP 50-75)

The following represents a brief description of the continuing volcanic activity of the almost unknown and inaccesible volcano El Sangay. A scientific group visited the volcano during the week of 24 May to 1 June 1975.

New blocky lava flows, that began before February 1975, continue advancing down the west side of this composite cone. The flows apparently originate in the summit crater (5,160 m) as suggested by the brilliant red glows seen in the crater at night and by occasional small explosions and blasts of dark gray smoke that are quickly dispersed by the high winds. The flows descend to about 3,800 m where they have fanned out and probably cover ~2 km2 in total area. The flow rock appears to be a basaltic andesite with olivine phenocrysts; milky white quartz xenocrysts are notably abundant to the total exclusion of all other types of inclusions.

The summit crater appears to be formed by at least two vents, one of which is emitting white clouds of vapor and sulfurous fumes almost continuously and another which emits infrequent blasts of dark gray clouds. The crater rim was continually being sandblasted by fine volcanic sand and ash, coming from the vents below, but no larger ejecta were observed. The strength of the fumes and the lack of visibility precluded a reconnaissance of the summit vents.

The west side (leeward side) of the volcano is covered by an approximate 70-m-thick sequence of thinly-bedded ashes, which probably corresponds to the renovation of activity in the 1940's after a 15 year dormancy. Since the 1940's the activity has been more Strombolian, marked by very muld but continuous ash eruptions and occasional lava flows. Evidence of past lahar activity is everywhere. The recent activity of El Sangay presents no danger to man.

Explosions, lava flows, and ashfall; two deaths following 10 August explosion

A recent expedition, 28 July-9 August, to the stratovolcano Sangay reports the following activity.

Mild explosive activity occurred at intervals of 6-12 hours with the expulsion of white, vapor-rich, sulfurous plumes that rose approximately 100 m. Very acidic rains were falling W of the cone. The NW side of the cone was covered by still-hot lava flows (basaltic andesite) from the last few years. A new lava flow was leaving the S crater and has descended W several hundred meters. A light coating of ash covered the snow on the SW side of the cone. No other activity was observed on the other sides of the volcano. It appeared that this activity has continued steadily from last year. A small parasitic cone of approximately 50 m height was recently discovered on the lower E flank. It is not presently active.

On 10 August an independent British team, which apparently included no geologist, reached the 3,700 m basecamp level on the volcano. Two days later six members ascended to within 300 m of the summit. At 1230 an explosion produced a black mushroom cloud that reached an estimated 300 m above the volcano and dropped ejecta (to 35 cm) on the group. Later, search parties found three injured, one dead, and another had not been found 5 days after the accident. Helicopter rescue attempts were abandoned on 18 August after two days of heavy snowfall.

. . . During overflights on 4 and 6 August, Maurice Krafft observed frequent ash emission from 1 of 4 WSW-ENE-trending vents in the summit area. The westernmost vent was filled by a blocky lava dome 15-20 m in diameter, partially covered by ash. ENE of the dome, explosions at least every 10 minutes from a 15-m-diameter crater produced thick black cauliflower-shaped ash columns 100-300 m high. Winds blew ash from these explosions to the SW, toward the dome. Each explosion also triggered small ash avalanches from deposits on the upper W and SW flanks. The largest of the four vents, ENE of the active crater, was 80-100 m across and contained two fumaroles that were emitting vapor. The fourth vent, 20-30 m in diameter and slightly N of the trend of the other 3 vents, was not active during the overflights.

Minard Hall reported that activity was generally similar when he visited the volcano in 1976. Although lava was oozing from the westernmost vent at that time, it had not yet built a dome.

Geologists from GEVA visited the volcano in June and August. Throughout June, only summit fumarolic activity was noted, but in early August, explosions every 5 minutes ejected small ash clouds. A warning was issued to aircraft flying in the vicinity of Sangay on 4 August at 2249. On 11 August, a new lava flow extended from the summit ~ 200 m below the crater rim. Blocks from the crumbling flow front rolled down the W and SW flanks to 4,400 m altitude. Larger avalanches from the flow front were observed on 12 August between 1400 and 1500. At 0005 on 13 August, explosions from a S-flank vent covered the volcano's S slope with red-hot lava blocks up to 1 m in diameter. Explosions ejecting blocks and ash continued until 0900. By 1600, the flow had moved to ~ 400 m below the crater rim and numerous blocks fell from the two lobes of the flow front.

From 24 November to 12 December 1995, the first detailed study of Sangay volcano (figures 1 and 2) was carried out by an Instituto Geofísico/ORSTOM team (Escuela Politécnica Nacional, Quito), with helicopter support from the Ecuadorian Army and the assistance of five local guides from Alao. During this time, activity was characterized by continuous fumarolic steaming, frequent phreatic explosions, occasional crater glow, and dome rockfalls. Previous reports from August 1976, August 1983, and June-August 1988 (SEAN 01:10, 08:07, and 13:08) identified four summit vents aligned WSW-ENE, which are here numbered from 1 to 4 going from W to E.

Figure 1. Present cone of Sangay in December 1995 viewed from the base camp 4.3 km SW. The recent pyroclastic-flow deposit on which the campsite is located is in the foreground, among the badlands corresponding to an older edifice. At the summit can be seen the W lava dome (Vent 1) and its now inactive lava tongues. Photo by M. Monzier, courtesy of ORSTOM.

Figure 2. View of the Sangay summit in December 1995 looking NE from the base camp showing the lava dome and associated lava flows from Vent 1. Behind this dome, a steam plume rises from the main crater (Vent 3). Photo by M. Monzier, courtesy of ORSTOM.

In 1976, Vent 1 consisted of a fracture from which lava was slowly issuing, but by August 1983 it had built a lava dome. This small dome was apparently more active in August 1988, and sent a lava flow 400 m down the W flank, where it split into two lobes. In late 1995 this dome was possibly still growing, and was the source of some fumarolic activity and many rockfalls, making the W and SW slopes of the cone dangerous to cross. Apparently there have been no new lava flows from this vent since August 1988. Vent 2, a small 15-m-diameter crater immediately ENE of Vent 1 has frequently been the site of explosive activity (1976 and 1983), but apparently was less active in 1988 and was quiet during the 1995 visit. The ENE crater (Vent 4) remained inactive but with occasional fumarolic activity.

Vent 3, at 80-100 m across, is the largest and deepest crater. In 1976 and 1983 only fumarolic activity was observed from this crater, but lava was reported in 1988. During the 1995 visit it was the site of frequent phreatic explosions, some separated by hours, others coming as often as every 26 minutes. Several explosions were followed by a rhythmic, pulsating roar that lasted for up to 50 oscillations. White vapor plumes, ejected with the audible explosions, rose several hundred meters above the summit. Light blue gas plumes and occasional red glow at night immediately above this crater implied the presence of lava. Frequent rockfalls from the upper S flank of the cone suggested that some lava may be escaping, breaking off, and rolling down the S slopes.

During the visit a portable MEQ-800 Sprengnether seismograph with a vertical, 1-Hz L4C geophone was operated at the La Playa base camp, 4.3 km SW of the main crater at 3,600 m elevation. A preliminary study of the smoked-paper seismograms showed three types of seismic signals, frequently associated with observed explosions in the crater (figures 3 and 4): tremor, long-period, and hybrid events. Tremor events had a monochromatic signature with a period of 1 second and lasted < 60 seconds. The long-period events had emergent arrivals and a constant period of ~0.7 seconds; they were often associated with observed explosions. Hybrid events began with a long-period event (0.7 seconds) and were followed by a signal similar to that of the tremor (1 second). Some hybrid events were associated with audible and observed explosions followed by a roar like pulsating, rhythmic exhalations. No local high-frequency events were detected.

Figure 3. Types of volcanic earthquakes at Sangay recorded by the seismic station 4.3 km SW in December 1995. Courtesy of ORSTOM.

Recent lavas and pyroclastic-flow, debris-flow, and lahar deposits are ubiquitous around the cone and testify to Sangay's nearly continuous activity. The site of the La Playa camp (figure 5) is on an andesitic pyroclastic-flow deposit containing bombs up to 4 m in diameter which was emplaced between 1956 and 1965. An accident with two fatalities happened in August 1976 (SEAN 01:10). A previously unreported accident occurred in December 1993 when the main crater exploded just as two mountaineers looked over its rim. Both were blinded by the heat and fragment impacts and remained lost in the jungle on the cone's lower slopes until rescued three days later.

In addition to the present cone (Sangay III), two previous edifices were identified and sampled, both of which had been destroyed by collapse. The remnant calderas are found on the E side of the present cone and are breached E toward the Amazon plain. Their probable avalanche deposits lie at the E foot of the cone. A preliminary geologic map of Sangay (figure 5) shows the three successive edifices and the two associated calderas. Edifice I is mainly built of lava, whereas edifices II and III contain both lava and pyroclastic deposits. The products of edifices I and II appear to be more varied in composition (greater differentiation) than those of Sangay III, where mafic andesites seem to predominate.

This isolated stratovolcano E of the Andean crest is one of Ecuador's most active volcanoes having been in frequent eruption for the past several centuries. The steep-sided glacier-covered volcano towers above the tropical jungle on the E side; on the other sides heavy rains have caused plains of ash to be sculpted into steep-walled canyons up to 600 m deep. The first historical eruption was reported in 1628, and more or less continuous eruptions took place from 1728 until 1916, and again from 1934 to the present.

Some conspicuous plumes during 2004-2005; climber's photos from January 2006

Our previous report was in 1996 (BGVN 21:03); this report covers the time interval January 2004 to January 2006. According to a 2004 annual summary on the Instituto Geofísico (IG) website, Sangay was one of the most active volcanoes in Ecuador, and has been in eruption for ~ 80 years. Its isolated location (figure 6) has meant it has been thought of as a relatively small hazard risk. For this reason, monitoring has been less than for other Ecuadorian volcanoes. Thermal, visual, and satellite monitoring during 2002-2004 confirmed the central crater as the source of frequent explosions and continuing steam-and-gas emissions.

Figure 6. Satellite imagery showing the region around the city of Riobamba (center) in Ecuador), including Sangay (lower right), Chimborazo (upper left), Tungurahua (upper right), and Licto (center) volcanoes. An eruption plume can be discerned coming from Tungurahua, but the date of the image is unknown. The city of Riobamba is about 50 km NW of Sangay. Courtesy of Google Earth.

During 2004 observers did not see lava flows or pyroclastic flows. An abnormally large eruption cloud was detected on 14 January 2004; it contained dominantly steam and gases, with minor ash content. Although only clearly detected and reported then, such events are thought to occur with considerable frequency.

Ramon and others (2006) summarized Sangay's activity as continuously erupting since 1934. Thermal images taken during the last three years showed that only one of the three summit craters was active and documented a lack of new, visible lava flows.

On 14 January 2004 a plume from Sangay was observed around 0500. The plume extended about 45 km E and most likely contained ash. During this time a hotspot was also visible on the satellite imagery. On 27 January 2004 a narrow ash plume emitted by Sangay rose to 6 km altitude and drifted SW.

On 1 May 2004, based on a pilot's report, the Washington VAAC noted that ash from an eruption at Sangay produced a plume to a height of ~ 6 km altitude at 1750. Ash was not visible on satellite imagery.

On 28 December 2004 around 0715 a plume from Sangay, most likely composed of steam with little ash, was detected. The plume was E of the volcano's summit at a height of ~ 6.4 km altitude. A hotspot was prominent on satellite imagery, but ash was more difficult to distinguish.

On 16 October 2005 around 0645 Sangay emitted an ash plume. The plume moved SSW very slowly, corresponding to a possible height of ~ 6.7 km altitude. By 0900 the plume was too thin to be visible on satellite imagery and thunderstorms developed in the area, further obscuring the ash cloud. Based on information from the IG, on 26 October 2005 the Washington VAAC noted that ash was seen over Sangay at 0758. No ash was visible on satellite imagery.

Climber's photo journal. Climbers Thorsten Boeckel and Martin Rietze created a website briefly describing a trek to Sangay's summit during 4-12 January 2006. Several of their posted photos from that trip appear here (figures 7-10; unfortunately, the photos, which are strikingly beautiful, were generally presented without much geographic context). The team included at least one local guide and was aided by horses. Settlements on the approach and return included the mountain village St. Eduardo, which they described as ~ 50 km S of Riobamba.

Figure 7. A vista of Sangay at nightfall in early January 2006. Direction of view is approximately WNW. Photo credit to Boeckel and Rietze.

Figure 8. Photograph documenting the climbers tent camp high on the snowbound slopes of Sangay during their descent. Exact location on Sangay unknown; this was labeled "day 4/5," and should correspond to 7 or 8 January 2006. Photo credit to Boeckel and Rietze.

Figure 9. A topographic high forming part of the Sangay structure, gently steaming, apparently seen from the summit. This corresponds to 7 or 8 January 2006. Photo credit to Boeckel and Rietze.

Figure 10. A crater on Sangay as seen by the climbers from the summit or upper flanks, described by them as the "snow covered east crater." This photo corresponds to 7 or 8 January 2006. Photo credit to Boeckel and Rietze.

Except for some degassing, the group saw no other activity. Although local residents indicated that the last eruption had occurred about 2 months prior to their visit, intermittent eruptions pose hazards to climbers; in 1976 two climbers were killed by explosions from Sangay (SEAN 01:10).

Our previous report on Sangay (BGVN 21:03) described occasional, but sometimes conspicuous, steam and/or ash plumes between January 2004 and January 2006. The current report continues coverage of plume emissions through December 2007.

Sangay has continued to erupt, sending ash plumes up to an altitude of about 11 km. A summary of plume activity is indicated in table 1. The information is from the Washington Volcanic Ash Advisory Center (VAAC), and is based on reports from the Guayaquil Meteorologic Watch Office, pilot reports, satellite imagery, and the Instituto Geofísico-Departamento de Geofísica (Escuela Politécnica Nacional). We did not receive any report of activity during the period February 2006 through September 2006, or during the first three months of 2008.

Table 1. Ash plume advisories about Sangay activity, October 2006 through December 2007. Courtesy of the Washington VAAC.

Date

Altitude (km)

Bearing

Remarks

11 Oct 2006

2.7

W

--

21 Oct 2006

6.7

--

--

22 Nov 2006

--

WNW

Hotspot visible on satellite imagery

02 Dec 2006

8.5

SW

--

23 Dec 2006

7.6

--

--

01 Jan 2007

5.2

--

--

14 Jan 2007

6.1

SW

--

28 Jan 2007

6.4

--

--

06 Feb 2007

9.1

SW

--

06-10 Feb 2007

6.1-9

Several

Hotspot at summit visible on satellite imagery

13 Feb 2007

--

--

Hotspot at summit visible on satellite imagery

23 Feb 2007

10.7

S

--

25 Feb 2007

6.4

SW

--

28 Feb 2007

7.6

--

--

02 Mar 2007

--

--

Weak hotspot visible on satellite imagery

05 Mar 2007

5.2-6.1

W

--

12-13 Mar 2007

7

W

Hotspot visible on satellite imagery

17 Mar 2007

5.2

--

Hotspot visible on satellite imagery

04 May 2007

5.2-7.6

--

--

05 May 2007

--

W

Possible narrow plume on satellite imagery

24 May 2007

7.3

--

--

03 Jul 2007

5.2-7.9

W

--

23 Jul 2007

5.5

W

Ash not detected by satellite imagery

24 Jul 2007

5.2

SW

--

28 Jul 2007

6.7-8.2

--

Weak hotspot visible on satellite imagery, but ash not detected

02 Aug 2007

5.5

W

Ash not detected by satellite imagery

19 Aug 2007

--

--

Clouds inhibited satellite imagery

08-09 Sep 2007

--

--

Ash not detected by satellite imagery

12 Oct 2007

7

W

--

26 Dec 2007

6.1

SW

--

26-27 Dec 2007

--

--

Thermal anomaly seen on satellite imagery

According to a report from the Instituto Geofísico, activity at Sangay increased at the end of 2006 through the beginning of 2007. They reported that a thermal anomaly was detected by satellite imagery during several days in December 2006. During that time, mountain guides near the volcano observed the fall of incandescent rocks down the volcano's flanks at night and a recent deposit of ash that was sufficiently deep to affect birds, rabbits, and other small animals. The report indicated that the Instituto Geofísico has not installed monitoring instrumentation near Sangay because of a significant logistics problem in maintaining them in this inhospitable area, and also because the area is uninhabited and thus poses no direct human risk. However, the report notes that because ash emissions from Sangay may pose problems for aircraft in the S, SE, and SW parts of the country, the Instituto maintains contact with the civil aviation authority.

Ash plumes were reported between October 2006 and December 2007 (BGVN 33:03). Thermal anomalies have been detected between 27 March and 4 December 2008 (table 2). A minor ash plume was seen on satellite imagery and by pilots drifting WNW on 24 September 2008.

Table 2. Thermal anomalies at Sangay based on MODIS-MODVOLC imaging during 1 January to 19 October 2008 (continued from the list in BGVN 33:03). No thermal anomalies were noted in 2008 prior to 27 March. Courtesy of Hawai'i Institute of Geophysics and Planetology (HIGP) Thermal Alerts System.

Our most recent reports on Sangay noted occasional steam and/or ash plumes between 11 October 2006 and 28 December 2007 (BGVN 33:03) and thermal anomalies between 27 March and 4 December 2008 (BGVN 34:01). The current report continues to tabulate this persistently erupting volcano's plumes from 28 December 2007 to 31 July 2009 (table 3), and thermal anomalies from 4 December 2008 to 10 August 2009 (table 4).

Table 3. Sangay ash plume activity, reported for 29 December 2008 to July 2009. NR signifies not reported and no plumes were observed 29-31 December 2008. TA is thermal anomaly. Courtesy of the Washington Volcanic Ash Advisory Center.

Date

Maximum Altitude

Bearing

Remarks

05 Jan 2009

7 km

S

--

09 Feb 2009

7.9

--

--

10 Mar 2009

5.5

W

TA detected

15 Jun 2009

--

WNW

TA reported by VAAC

26 Jun 2009

7.6

W

--

23 Jul 2009

7.9

--

--

Table 4. Thermal anomalies at Sangay based on MODIS-MODVOLC data during 4 December 2008 to 10 August 2009 (continued from the list in BGVN 34:01). Courtesy HIGP Thermal Alerts System.

Occasional ash plumes and thermal anomalies continue into at least February 2010

Sangay, which has been in near constant eruption for centuries, continued its eruptive activity into 2010. Previous reports on Sangay (BGVN 33:03, 34:01, and 34:06) had documented occasional ash plumes through 31 July and thermal anomalies through 10 August 2009. After almost two months with no indications of observed by satellite, both plumes and thermal anomalies resumed on 4 October 2009 (tables 5 and 6). Intermittent observations of plumes and MODVOLC thermal alerts were made every month afterwards through February 2010.

Table 5. Sangay ash plumes recorded during August 2009-February 2010. TA indicates a thermal anomaly noted by a VAAC analyst. No plumes were observed during 24 July-3 October 2009. Courtesy of the Washington Volcanic Ash Advisory Center (VAAC).

Date

Maximum Altitude

Bearing

Remarks

04 Oct 2009

5.2-7.6 km

W

--

15 Oct 2009

--

SW

Seen for ~15 km

16 Nov 2009

--

WNW

TA detected

01 Dec 2009

7.9 km

W

Eruption reported

18, 21 Dec 2009

7.9 km

W

TAs detected

02-03 Jan 2010

7 km

NW

TAs 2-4 January

14 Jan 2010

7.3 km

--

--

02 Feb 2010

8.2 km

--

--

22 Feb 2010

7.6 km

--

--

Table 6. Thermal alerts issued for Sangay by the MODVOLC system during August 2009-February 2010 (continued from the list in BGVN 34:06). Courtesy HIGP Thermal Alerts System.

The last report discussed observations of ash plumes and MODVOLC thermal alerts at Sangay through February 2010 (BGVN 35:01). Intermittent reporting indicated that similar activity continued through at least February 2011, with plumes reaching up to 7.6 km altitude (table 7). Clouds obscured the view at times, and plumes were reported primarily by pilots and were sometimes visible on satellite imagery.

Table 7. Plumes reported at Sangay during April 2010-February 2011. No plumes were noted during March 2011. Courtesy of the Washington VAAC.

The MODVOLC alert system issued thermal alerts for Sangay monthly during March 2010 through early October 2010. Then, alerts were absent until 11 January 2011 (table 8).

Table 8. Thermal alerts issued for Sangay by the MODVOLC system during March 2010-20 March 2011 (continued from the list in BGVN 35:01). The system uses the MODIS instrument on the Terra and Aqua satellites. Courtesy MODVOLC Thermal Alerts System.

Ongoing thermal anomalies, ash fall and plumes continued through May 2013

Previously reported activity from Sangay volcano (figure 11) included ash plumes and elevated temperatures (BGVN 36:01). In this report, we note that similar activity persisted during August 2011-May 2013. We highlight low-level unrest that was primarily detected with remote sensing instruments and pilot reports.

Figure 11. This GoogleEarth image of Sangay includes an inset (below) from Landsat 7 acquired on 16 September 2001. The exaggerated blue color distinguishes the snow-and-ice covered summit from regional clouds (white with magenta in locations where the cloud is thinning). Note the gray area in the SE sector, an eruptive event had recently occurred that covered (or potentially melted) the typically symmetrical snowcover. The scale bar is approximate. Courtesy of GoogleEarth and USGS/NASA.

Ash plumes during 2011-2013. Notices from the Washington Volcanic Ash Advisory Center (VAAC) during this reporting period were primarily based on pilot reports and a weather station located in Guayaquil (MWO). There were seven significant plumes visible with satellite images; those plumes reached altitudes of altitudes 6-8 km a.s.l. (table 9). Ash plumes drifted to a maximum distance of 20 km from the summit.

A 25 January 2012 report from Instituto Geofísico-Escuela Politécnica Nacional (IG) (Special Report No. 01-2012) stated that activity at Sangay had intensified since 23 January. Pilot reports on 23 January were noted by the Washington VAAC with observations of ash moving SSE. Satellite images from 24 January noted thermal anomalies.

Table 9.Washington VAAC reports for Sangay during August 2011-May 2013. The following abbreviations are used: volcanic ash (VA) and meteorological watch observatory (MWO). No VAAC reports were released during June-August 2013, the remaining duration of this report. Courtesy of VAAC.

YEAR

DATE

TYPE OF PLUME

ALTITUDE

BEARING

REMARKS

2011

2-Aug

possible va emission

6 km

na

Pilot report of VA to 6 km altitude

2011

11-Oct

possible va emission

na

na

Guayaquil weather station

2011

25-Oct

ash plume

6 km

E 9-19 km/h

Satellite images showed a plumes of gases and possible VA 19 km wide

2011

20-Nov

possible va emission

na

na

Pilot report and MWO OF VA

2012

8-Jan

possible va emission

na

na

Guayaquil weather station

2012

23-Jan

possible va emission

na

na

Pilot report and MWO of VA

2012

24-Jan

possible va emission

na

na

Weak hotspot in images

2012

22-Mar

possible va emission

na

na

Pilot report and MWO of VA

2012

23-Mar

possible va emission

na

na

Pilot report of VA

2012

11-May

possible va emission

na

na

Guayaquil weather station

2012

28-May

possible va emission

na

na

Guayaquil weather station

2012

4-Jun

possible va emission

8 km

na

Pilot report 8 km altitude and MWO of VA

2012

6-Jun

possible va emission

6 km

na

Pilot report 6 km altitude and MWO of VA

2012

10-Jun

possible va emission

na

na

Pilot report and MWO of VA

2012

11-Jun

possible va emission

na

na

Guayaquil weather station

2012

4-Jul

possible va emission

na

na

Pilot report of VA and MWO; a hotspot detected in multispectral imagery

2012

5-Jul

na

na

na

Pilot report of VA; a hotspot visible in multispectral imagery

2012

6-Jul

na

na

na

Weak hotspot in images

2012

20-Jul

possible va emission

na

na

Pilot report of VA

2012

21-Jul

possible va emission

na

na

Guayaquil weather station

2012

28-Jul

small emission

7 km

W

Pilot report; in satellite images a small burst of gas through cloud layers was observed.

2013

25-Jan

possible va emission

na

na

Pilot report and MWO of VA; weak hotspot in images

2013

26-Jan

possible emission of gases and va

na

na

weak hotspot in images

2013

22-Feb

possible va emission

na

na

Pilot report and MWO of VA

2013

24-Feb

possible va emission

na

na

Pilot report and MWO of VA

2013

11-Apr

ash plume

6 km

W

Visible satellite images showed a VA plume; event should dissipate over the next 3 hours.

2013

26-Apr

ash plume

8 km

SW 9 km/h

A couple of weak VA emissions within 20 km of the summit; a hotspot was observed in images.

2013

23-May

possible va emission

na

na

Pilot report W at 8 km altitude and MWO of VA

Elevated temperatures from the summit. Modvolc detected hotspots from February 2010 to early May 2013 (table 10). The elevated temperatures were detected around the summit area with as many as 3 pixels but typically one pixel per observation (figure 12). Hotspots were no longer visible after 4 May through August 2013.

Table 10.Hotspots from the region of Sangay were detected consistently during February 2010 through early May 2013. The Modvolc system uses the MODIS instrument on the Terra and Aqua satellites. Courtesy MODVOLC Thermal Alerts System.

Date (UTC)

Time (UTC)

Pixels

Satellite

2/25/2010

03 45

1

Terra

3/15/2010

03 30

1

Terra

4/30/2010

03 45

1

Terra

5/16/2010

03 45

1

Terra

6/3/2010

03 30

1

Terra

7/12/2010

03 40

1

Terra

8/18/2010

06 55

1

Aqua

9/28/2010

06 50

2

Aqua

9/30/2010

03 35

1

Terra

10/2/2010

03 25

1

Terra

10/7/2010

03 45

1

Terra

1/11/2011

03 45

1

Terra

3/2/2011

03 30

1

Terra

6/6/2011

03 30

2

Terra

6/29/2011

06 35

1

Aqua

7/15/2011

03 35

2

Terra

7/20/2011

06 55

1

Aqua

8/7/2011

03 45

1

Terra

8/14/2011

03 50

1

Terra

8/23/2011

06 40

1

Aqua

8/25/2011

06 30

1

Aqua

10/5/2011

06 20

1

Aqua

10/5/2011

15 45

1

Terra

10/31/2011

07 00

1

Aqua

12/29/2011

06 40

1

Aqua

1/5/2012

03 50

1

Terra

1/7/2012

03 40

1

Terra

1/25/2012

03 25

2

Terra

1/25/2012

06 25

1

Aqua

2/8/2012

06 35

1

Aqua

2/21/2012

03 05

3

Terra

3/25/2012

06 50

1

Aqua

4/10/2012

03 50

1

Terra

4/12/2012

03 35

1

Terra

5/25/2012

18 35

1

Aqua

6/6/2012

03 45

1

Terra

7/17/2012

06 35

1

Aqua

7/26/2012

03 30

1

Terra

7/29/2012

04 00

2

Terra

9/17/2012

06 45

1

Aqua

9/19/2012

03 35

1

Terra

2/24/2013

03 50

1

Terra

3/25/2013

03 20

1

Terra

5/3/2013

03 25

1

Terra

5/4/2013

07 05

1

Aqua

Figure 12. From 4 May 2013 to 4 May 2012, Modvolc detected 11 hotspots in the region of Sangay. These elevated temperatures were centered on and located within 3 km of the summit area. Courtesy of HIGP.

Satellite images during 2012-2013. Significant cloudcover in the region of Sangay prohibited clear satellite views of volcanic activity. In Figure 13, four images were chosen for relatively unobstructed views, however, due to technical problems with a sensor onboard Landsat 7, black bands interfere with the images. Despite these challenges, bright snow is easily distinguished from the summit area and the disruptions of the typically white (altered to blue for higher contrast) summit suggest processes such as ashfall, lahars, or melting causing new exposures of underlying rock. Ash events were frequently documented as late as 23 May 2013 and it is clear in the 8 August 2013 image that the summit snow was no longer significantly disturbed.

Figure 13. Satellite images from Landsat 7 (12 July 2012, 10 April 2013, and 26 April 2013) and Landsat 8 (8 August 2013) captured views of the changing conditions at Sangay. Snow and ice at the summit appears as bright blue while cloudcover is typically white with some magenta fringes; recent ashfall, lahars, or melting events have disrupted the symmetrical snow region in these images except for the image from 8 August 2013. Courtesy of USGS/NASA.

Previously reported activity from Sangay volcano (figure 11) included ash plumes as late as 23 May 2013 and satellite infrared thermal alerts ending in early May 2013 (BGVN 36:01). In that previous report, satellite thermal alerts from the MODVOLC system were noted to have persisted and as late as 4 May 2013. That lack of alerts continued as late as 16 July 2013 when the MODVOLC website was last checked. Since that reporting, there have been no new updates regarding Sangay on the website of the Instituto Geofisico (IG), the aviation reports have not mentioned Sangay, and other news of Sangay behavior has also been generally lacking.

Figure 11. (Inset at bottom) A regional map showing Sangay with respect to large rivers and other features surrounding Sangay. Orange line is the PanAmerican highway, which passes near Río Bamba on the map's N. Major rivers (blue) are primary routes of lahars. (Main map) A hazards map for Sangay made with hazards focus and compiling the results of multiple kinds of modeling. Key (in Spanish) notes that the upper three colors were based on slope angle (H/L) with text noting gradation of hazards in those regions from pyroclastic flows, lava flows, ash falls, volcanic bombs, rock falls, and proximal lahars. The lower three colors on the key represent inferred gradations of lahar hazard at distance from the volcano. Dashed envelopes in red refer to boundaries for small and moderate sizes of ash falls. White line shows inferred boundary for an E directed debris avalanche. Base map is from the Instituto Geografico Militar (IGM). Taken from an online poster by Ordóñez and others, 2014).

Absence of MODVOLC and aviation alerts does not necessarily translate to a lack of eruptions. The MODVOLC system imposes a reasonably high threshold to the infrared data acquired from space. Factors such as weather conditions, snow pack, and geometry of the vent area may play a role. Emissions of spatter, ash fall, and small pyroclastic flows could easily be missed. Assessments are generally best made in conjunction with information at the volcano. The current eruption began on 8 August 1934 and is thus far confirmed only through 23 May 2013.

Hazard modeling and products. In late 2013 to early 2014 IG released a poster discussing Sangay hazards (Ordóñez and others, 2014), some of the results of which we reprint here (figures 11, 12, and 13). Figure 11 contains IGEPN's recently published a map of volcanic hazards associated with Sangay, which resides in the Cordillera Real between the cities of Río Bamba and Macas. The IG and others have generally considered Sangay one of the most active volcanoes in South America. The poster noted historical records of its eruptive activity dating back to 1628 (Hall, 1977) and in the last century some important periods of activity were recorded during 1903, 1934-1937, 1941-1942, 1975-1976, and 1995 to the present (Monzier et al.. 1999). Observations of surface activity carried out in the past 40 years allowed scientists to recognize some important morphological changes at the summit of the volcano, including the emergence of new craters, dome growth, extrusion of lava flows, local explosions and ash emissions, and relatively small pyroclastic flows.

Figure 12. Modeled ash fall blanket from a hypothetical eruption at Sangay of moderate size. The key (in Spanish) refers to the colors in the key and on the isopach map, with thicknesses in millimeters. Taken from an online poster by Ordóñez and others (2014).

Figure 13. Modeled ash fall blanket from a hypothetical eruption at Sangay of large size. The key (in Spanish) refers to the colors in the key and on the isopach map, with thicknesses in millimeters. Taken from an online poster by Ordóñez and others (2014).

A larger suite of volcanic hazards models is not shown here but includes results VolcFlow. Ash3D, Tephra2, and LAHARZ. The data used for the simulations were obtained from the few geological studies in this volcano (Hall, 1977; Monzier et al, 1999; Johnson et al, 2003). Sangay is judged in some ways analogous to Tungurahua volcano, because of its chemical composition, and it similar lava rheology and eruptive style of volcanic flows.

During August-September 2013, IG installed seismic monitoring instruments (broad band and infrasound ) and for the measurement of sulfur dioxide (SO2) in the southwestern flank of the volcano Sangay. These tools facilitate the monitoring of internal and surface activity of the volcano which will give an early warning of a potential hazards.

Figures 12 and 13 show the respective modeled results for a moderate and large eruption. To define the zones affected by ash fall, the modeling used the following computer routines based on assumptions and approaches discussed in the literature: Ash3d (Mastin and others, 2012) and Tephra2 (Banadonna and others, 2005). Some input data came from inferences and interpretations of descriptions by Monzier and others (1999) and from analogy with recent eruptions at Tungurahua. Plume heights were assumed to reach 10-15 km in altitude and the magma volumes in the plumes were assumed to be on the order of 0.001-0.005 km3 (dense-rock equivalent, DRE). Wind field data came from the Global Forecast System (NOAA, US National Weather Service, Environment Modeling Center). LAHARZ (Schilling, 1998), a modeling approach, was also taken to estimate the extent and coverage of lahars seen in figure 11. (The poster includes other maps on this topic as well.)

Ecuador's Sangay, isolated on the east side of the Andean crest, has exhibited frequent eruptive activity over the last 400 years. Its remoteness has made ground observations difficult until recent times, and thus most information has come from aviation reports from the Washington Volcanic Ash Advisory Center (VAAC) and MODIS (Moderate Resolution Imaging Spectroradiometer) satellite-based data. Thermal anomaly information is reported by the University of Hawaii's MODVOLC system and the Italian MIROVA Volcano HotSpot Detection System. Ecuador's Instituto Geofísico (IG) issues periodic Special Reports of activity. This report summarizes the intermittent nature of the eruptions from 2011-2013, and covers renewed activity during January 2015 through July 2017.

Summary of activity during 2011-2013. Activity during 2011 (figure 14) began with a continuation of the intermittent ash emissions and thermal anomalies that persisted throughout 2010 (BGVN 36:01). Ash plumes during January and February 2011 were reported at typical altitudes between 6 and 8 km; thermal alerts appeared once each during January and March. No activity was reported after 2 March until a new series of thermal alerts began more than 3 months later on 6 June 2011; they were intermittent from then through 19 September 2012, with reports occurring during 1-4 days of all but three months. Ash emissions were also intermittent during this time, with VAAC reports issued during eight of the months from 2 August 2011-28 July 2012 for plumes reported at altitudes of 6-8 km. They also generally occurred during 1-4 days of the month. A four-month break in activity followed until ash plumes were reported on 25 January 2013; they were intermittent until 24 May 2013. MODVOLC thermal anomalies were also reported during this time, on 2 February, 25 March, and 3-4 May.

Figure 14. Summary chart of ash emissions and thermal anomalies reported from Sangay during January 2010 to early August 2017. Red bars show eruptive periods where there are reports of either ash plumes or thermal anomalies without a lack of observed activity for more than 3 months. Rows with pink cells indicate dates with thermal anomalies (MODVOLC or MIROVA). Rows with blue cells indicate dates with ash emissions as reported by the Washington VAAC. A range of dates means that activity occurred at least on those two dates, but may not have been continuous. Data courtesy of Washington VAAC, HIGP MODVOLC Thermal Alerts System, and MIROVA.

Summary of activity during January 2015-July 2017. After 19 months of quiet from June 2013 through December 2014, an ash plume reported on 19 January 2015 marked the beginning of a new eruptive episode that included ash plumes, lava flows, and block avalanches between 19 January and 7 April 2015. The next reported activity included both ash emissions and thermal anomalies observed almost a year later on 25 March 2016, although IG had reported increases in seismicity during the previous two weeks. Ash emissions and thermal anomalies were intermittent through 16 July 2016. There was a single thermal anomaly seen in MIROVA data on about 10 October and a brief ash emission occurred during 16-17 November 2016, after which Sangay was quiet until a new episode started on 20 July 2017 that was ongoing into August.

Activity during January-April 2015. After a 19-month period of no reported activity (since May 2013), ash emissions were again seen beginning on 18 January 2015 when an ash plume rose to 6.4 km altitude and drifted SW. Additional plumes on 25 January and 4 February rose to 7.3 km and 6.7 km, respectively, and drifted less than 20 km SW (figure 15). Ash plumes primarily observed by pilots between 27 February and 16 March were generally not visible in satellite images due to weather clouds. During this episode, MODVOLC thermal alerts were reported on 26 January; 7, 21, 23 and 27 February; 2,4,18, and 27 March; and 1, 3, and 7 April.

In a March 2015 report, IG noted that new lava flows and block-avalanche deposits had been emplaced during January and February 2015. The lava flows descended the SE flank about 900 m (figure 16). Two areas of deposits from block avalanches and ashfall extended 2.5 km ESE from the lava front, and 1.5 km down the S flank. According to IG, there were 21 thermal anomalies identified in MIROVA during 31 January-25 February 2015.

Figure 16. Locations of lava flows and block-avalanche deposits at Sangay that were emplaced during January and February 2015. The new lava flows are shown in red. The ash and block-avalanche deposits are shown in stippled yellow/green. Courtesy of IG (Informe Especial del Volcan Sangay No 1, 16 March 2015).

Activity during March-November 2016. IG reported an increase in seismicity on 5 March 2016, after ten months of no reported activity. An explosion signal was followed by harmonic tremor on 9 March, and IG noted that both a thermal anomaly and an emission drifting S were identified in NOAA satellite images. They inferred that increased seismic "explosion" signals on 14 March were indicative of ash-and-gas emissions, although weather clouds prohibited visual confirmation. Ash emissions rising to 6.1 km altitude were first reported by the Guayaquil MWO on 25 March 2016; they noted two more emissions on 27 and 28 March rising to similar altitudes (7.6 and 6.4 km, respectively), but cloudy weather prevented satellite confirmation. Plumes reported on nine days during April rose to similar altitudes (ranging from 5.5-7 km) and extended 18-30 km N or NW from the summit. A series of daily emissions occurred from 30 April-7 May. The emissions included a plume on 2 May that extended 120 km NW, and one on 6 May that rose to 8.2 km altitude and extended approximately 55 km SW before dissipating. Ash-bearing plumes were reported on 10 more days during the rest of May.

Although no more ash plumes were reported until 16 July 2016, MODVOLC thermal alerts were persistent every month beginning on 25 March and lasting through 5 July (see figure 14 above). The MIROVA data for this period also clearly show persistent thermal anomalies (figure 17). A short-lived eruption event during 16-17 November 2016 consisted of an ash emission that rose to 6.1 km altitude and drifted as far as 290 km SE.

Figure 17. Thermal anomaly data from MIROVA for the year ending on 18 January 2017 at Sangay, showing the eruptive episode of March-July 2016, and a brief anomaly on about 10 October 2016; late October-November anomalies are more than 20 kilometers from the summit and unrelated to volcanism. Courtesy of MIROVA.

Activity beginning July 2017. A new eruptive episode began on 20 July 2017, after eight months without major surface activity. Low-energy ash emissions rising to 3 km above the crater, incandescent block avalanches on the ESE flank (figure 18), and a possible new lava flow were reported by IG. The Washington VAAC reported an ash emission on 20 July rising to 8.2 km altitude and drifting about 80 km W. A plume was reported on 1 August by the Guyaquil MWO but obscured by clouds in satellite images, and a plume on 2 August was seen in webcam images (figure 19).

Figure 18. Incandescent blocks roll down the ESE flank of Sangay during the early morning of 1 August 2017. Courtesy of IG (Informe Especial del Volcán Sangay-2017-No 1, 3 August 2017).

This compilation of synonyms and subsidiary features may not be comprehensive. Features are organized into four major categories: Cones, Craters, Domes, and Thermal Features. Synonyms of features appear indented below the primary name. In some cases additional feature type, elevation, or location details are provided.

Synonyms

Sanagay | Sangai | Macas, Volcan de

Cones

Feature Name

Feature Type

Elevation

Latitude

Longitude

Verdeloma

Stratovolcano

Basic Data

Volcano Number

Last Known Eruption

Elevation

LatitudeLongitude

352090

2017 CE

5286 m / 17338 ft

2.005°S
78.341°W

Volcano Types

Stratovolcano
Caldera(s)

Rock Types

MajorAndesite / Basaltic Andesite

MinorDacite
Basalt / Picro-Basalt

Tectonic Setting

Subduction zoneContinental crust (> 25 km)

Population

Within 5 kmWithin 10 kmWithin 30 kmWithin 100 km

231
1,675
15,130
1,355,275

Geological Summary

The isolated Sangay volcano, located east of the Andean crest, is the southernmost of Ecuador's volcanoes, and its most active. The dominantly andesitic volcano has been in frequent eruption for the past several centuries. The steep-sided, 5230-m-high glacier-covered volcano grew within horseshoe-shaped calderas of two previous edifices, which were destroyed by collapse to the east, producing large debris avalanches that reached the Amazonian lowlands. The modern edifice dates back to at least 14,000 years ago. It towers above the tropical jungle on the east side; on the other sides flat plains of ash have been sculpted by heavy rains into steep-walled canyons up to 600 m deep. The earliest report of a historical eruption was in 1628. More or less continuous eruptions were reported from 1728 until 1916, and again from 1934 to the present. The almost constant activity has caused frequent changes to the morphology of the summit crater complex.

References

The following references have all been used during the compilation of data for this volcano, it is not a comprehensive bibliography.

Deformation History

There is no Deformation History data available for Sangay.

Emission History

There is no Emissions History data available for Sangay.

Photo Gallery

The isolated Sangay volcano towers above tropical jungles east of the Andean crest. Seen here from the NE, it is one of Ecuador's most active volcanoes and has been in frequent eruption during the past several centuries. The steep-sided, glacier-covered volcano has been constructed within the older Verdeloma somma to the south. Historical eruptions were first reported in 1628. More-or-less continuous eruptions took place from 1728 until 1916, and again from 1934 until the present.

Photo by Minard Hall, 1976 (Escuela Politécnica Nacional, Quito).

Activity seen in this August 1976 view of the west flank of Sangay volcano is typical of a long-term eruption that began in 1934. An ash plume rises from one of several summit craters. Much of the dark area on the western flank is a shadow, but a dark lava flow can be seen descending the slopes of the volcano. Frequent explosive eruptions and occasional lava flows have constructed Ecuador's most symmetrical volcano. It rises to over 5200-m altitude above the jungles of the western Amazon basin.

A dark lava flow descends the upper western flank of Sangay volcano in 1976. The lava flow originated from the southernmost of several small craters at Sangay's summit. This frequently cloud-covered volcano is Ecuador's most active. Almost continuous minor explosive activity took place from 1728 until about 1916, and resumed in 1934. Occasional larger eruptions produced detonations heard hundreds of km away.

Photo by Minard Hall, 1976 (Escuela Politécnica Nacional, Quito).

Steam clouds rise above two of three summit craters at Ecuador's Sangay volcano. Continual eruptions since 1934 have frequently modified the morphology of the volcano's summit. At the time of this 1976 view from the east, a lava flow from the southernmost crater (right) was descending the western flank.

Smithsonian Sample Collections Database

Affiliated Sites

The DECADE portal, still in the developmental stage, serves as an example of the proposed interoperability between The Smithsonian Institution's Global Volcanism Program, the MAGA Database, and the EarthChem Geochemical Portal. The Deep Earth Carbon Degassing (DECADE) initiative seeks to use new and established technologies to determine accurate global fluxes of volcanic CO2 to the atmosphere, but installing CO2 monitoring networks on 20 of the world's 150 most actively degassing volcanoes. The group uses related laboratory-based studies (direct gas sampling and analysis, melt inclusions) to provide new data for direct degassing of deep earth carbon to the atmosphere.

WOVOdat is a database of volcanic unrest; instrumentally and visually recorded changes in seismicity, ground deformation, gas emission, and other parameters from their normal baselines. It is sponsored by the World Organization of Volcano Observatories (WOVO) and presently hosted at the Earth Observatory of Singapore.

Middle InfraRed Observation of Volcanic Activity (MIROVA) is a near real time volcanic hot-spot detection system based on the analysis of MODIS (Moderate Resolution Imaging Spectroradiometer) data. In particular, MIROVA uses the Middle InfraRed Radiation (MIR), measured over target volcanoes, in order to detect, locate and measure the heat radiation sourced from volcanic activity.

Using infrared satellite Moderate Resolution Imaging Spectroradiometer (MODIS) data, scientists at the Hawai'i Institute of Geophysics and Planetology, University of Hawai'i, developed an automated system called MODVOLC to map thermal hot-spots in near real time. For each MODIS image, the algorithm automatically scans each 1 km pixel within it to check for high-temperature hot-spots. When one is found the date, time, location, and intensity are recorded. MODIS looks at every square km of the Earth every 48 hours, once during the day and once during the night, and the presence of two MODIS sensors in space allows at least four hot-spot observations every two days. Each day updated global maps are compiled to display the locations of all hot spots detected in the previous 24 hours. There is a drop-down list with volcano names which allow users to 'zoom-in' and examine the distribution of hot-spots at a variety of spatial scales.

EarthChem develops and maintains databases, software, and services that support the preservation, discovery, access and analysis of geochemical data, and facilitate their integration with the broad array of other available earth science parameters. EarthChem is operated by a joint team of disciplinary scientists, data scientists, data managers and information technology developers who are part of the NSF-funded data facility Integrated Earth Data Applications (IEDA). IEDA is a collaborative effort of EarthChem and the Marine Geoscience Data System (MGDS).